The influence of continental ice, atmospheric CO2, and land albedo on the climate of the last glacial maximum

Abstract

The contributions of expanded continental ice, reduced atm9spheric CO2, and changes in land albedo to the maintenance of the climate of the last glacial maximum (LGM) are examined. A series of experiments is perform- ed using an atmosphere-mixed layer ocean model in which these changes in boundary conditions are incorporated either singly or in combination. The model used has been shown to produce a reasonably reaJistic simulation of the reduced temperature of the LGM (Manabe and Broccoli 1985~). By comparing the results from pairs of ex- periments, the effects of each of these envirornnental changes can be determined. Expanded continental ice and reduced atmospheric CO2 are found to have a substantial impact on global mean temperature. The ice sheet effect is confined almost ex- clusively to the Northern Hemisphere, while lowered CO2 cools both hemispheres. Changes in land albedo over ice- free areas have only a minor thermal effect on a global basis. The reduction of CO2 content in the atmosphere is the primary contributor to the cooling of the Southern Hemisphere. The model sensitivity to both the ice sheet and CO2 effects is characterized by a high latitude amplification and a late autumn and early winter maximum.